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Subject[PATCH 2/4 v2] exfat: separate the boot sector analysis
Date
Separate the boot sector analysis to read_boot_sector().
Furthermore, add a strict consistency check, because overlapping areas
can cause serious corruption.

Signed-off-by: Tetsuhiro Kohada <kohada.t2@gmail.com>
---
Changes in v2:
- rebase with patch 'optimize dir-cache' applied

fs/exfat/exfat_raw.h | 1 +
fs/exfat/super.c | 96 +++++++++++++++++++++++---------------------
2 files changed, 52 insertions(+), 45 deletions(-)

diff --git a/fs/exfat/exfat_raw.h b/fs/exfat/exfat_raw.h
index b373dc4e099f..65f884785192 100644
--- a/fs/exfat/exfat_raw.h
+++ b/fs/exfat/exfat_raw.h
@@ -15,6 +15,7 @@

#define VOL_CLEAN 0x0000
#define VOL_DIRTY 0x0002
+#define ERR_MEDIUM 0x0004

#define EXFAT_EOF_CLUSTER 0xFFFFFFFFu
#define EXFAT_BAD_CLUSTER 0xFFFFFFF7u
diff --git a/fs/exfat/super.c b/fs/exfat/super.c
index e60d28e73ff0..95909b4d5e75 100644
--- a/fs/exfat/super.c
+++ b/fs/exfat/super.c
@@ -366,25 +366,20 @@ static int exfat_read_root(struct inode *inode)
return 0;
}

-static struct boot_sector *exfat_read_boot_with_logical_sector(
- struct super_block *sb)
+static int exfat_calibrate_blocksize(struct super_block *sb, int logical_sect)
{
struct exfat_sb_info *sbi = EXFAT_SB(sb);
- struct boot_sector *p_boot = (struct boot_sector *)sbi->boot_bh->b_data;
- unsigned short logical_sect = 0;
-
- logical_sect = 1 << p_boot->sect_size_bits;

if (!is_power_of_2(logical_sect) ||
logical_sect < 512 || logical_sect > 4096) {
exfat_err(sb, "bogus logical sector size %u", logical_sect);
- return NULL;
+ return -EIO;
}

if (logical_sect < sb->s_blocksize) {
exfat_err(sb, "logical sector size too small for device (logical sector size = %u)",
logical_sect);
- return NULL;
+ return -EIO;
}

if (logical_sect > sb->s_blocksize) {
@@ -394,24 +389,20 @@ static struct boot_sector *exfat_read_boot_with_logical_sector(
if (!sb_set_blocksize(sb, logical_sect)) {
exfat_err(sb, "unable to set blocksize %u",
logical_sect);
- return NULL;
+ return -EIO;
}
sbi->boot_bh = sb_bread(sb, 0);
if (!sbi->boot_bh) {
exfat_err(sb, "unable to read boot sector (logical sector size = %lu)",
sb->s_blocksize);
- return NULL;
+ return -EIO;
}
-
- p_boot = (struct boot_sector *)sbi->boot_bh->b_data;
}
- return p_boot;
+ return 0;
}

-/* mount the file system volume */
-static int __exfat_fill_super(struct super_block *sb)
+static int exfat_read_boot_sector(struct super_block *sb)
{
- int ret;
struct boot_sector *p_boot;
struct exfat_sb_info *sbi = EXFAT_SB(sb);

@@ -424,51 +415,36 @@ static int __exfat_fill_super(struct super_block *sb)
exfat_err(sb, "unable to read boot sector");
return -EIO;
}
-
- /* PRB is read */
p_boot = (struct boot_sector *)sbi->boot_bh->b_data;

/* check the validity of BOOT */
if (le16_to_cpu((p_boot->signature)) != BOOT_SIGNATURE) {
exfat_err(sb, "invalid boot record signature");
- ret = -EINVAL;
- goto free_bh;
- }
-
-
- /* check logical sector size */
- p_boot = exfat_read_boot_with_logical_sector(sb);
- if (!p_boot) {
- ret = -EIO;
- goto free_bh;
+ return -EINVAL;
}

/*
- * res_zero field must be filled with zero to prevent mounting
+ * must_be_zero field must be filled with zero to prevent mounting
* from FAT volume.
*/
- if (memchr_inv(p_boot->must_be_zero, 0,
- sizeof(p_boot->must_be_zero))) {
- ret = -EINVAL;
- goto free_bh;
- }
+ if (memchr_inv(p_boot->must_be_zero, 0, sizeof(p_boot->must_be_zero)))
+ return -EINVAL;

- p_boot = (struct boot_sector *)p_boot;
- if (!p_boot->num_fats) {
+ if (p_boot->num_fats != 1 && p_boot->num_fats != 2) {
exfat_err(sb, "bogus number of FAT structure");
- ret = -EINVAL;
- goto free_bh;
+ return -EINVAL;
}

sbi->sect_per_clus = 1 << p_boot->sect_per_clus_bits;
sbi->sect_per_clus_bits = p_boot->sect_per_clus_bits;
- sbi->cluster_size_bits = sbi->sect_per_clus_bits + sb->s_blocksize_bits;
+ sbi->cluster_size_bits = p_boot->sect_per_clus_bits +
+ p_boot->sect_size_bits;
sbi->cluster_size = 1 << sbi->cluster_size_bits;
sbi->num_FAT_sectors = le32_to_cpu(p_boot->fat_length);
sbi->FAT1_start_sector = le32_to_cpu(p_boot->fat_offset);
- sbi->FAT2_start_sector = p_boot->num_fats == 1 ?
- sbi->FAT1_start_sector :
- sbi->FAT1_start_sector + sbi->num_FAT_sectors;
+ sbi->FAT2_start_sector = le32_to_cpu(p_boot->fat_offset);
+ if (p_boot->num_fats == 2)
+ sbi->FAT2_start_sector += sbi->num_FAT_sectors;
sbi->data_start_sector = le32_to_cpu(p_boot->clu_offset);
sbi->num_sectors = le64_to_cpu(p_boot->vol_length);
/* because the cluster index starts with 2 */
@@ -483,15 +459,45 @@ static int __exfat_fill_super(struct super_block *sb)
sbi->clu_srch_ptr = EXFAT_FIRST_CLUSTER;
sbi->used_clusters = EXFAT_CLUSTERS_UNTRACKED;

- if (le16_to_cpu(p_boot->vol_flags) & VOL_DIRTY) {
- sbi->vol_flag |= VOL_DIRTY;
- exfat_warn(sb, "Volume was not properly unmounted. Some data may be corrupt. Please run fsck.");
+ /* check consistencies */
+ if (sbi->num_FAT_sectors << p_boot->sect_size_bits <
+ sbi->num_clusters * 4) {
+ exfat_err(sb, "bogus fat length");
+ return -EINVAL;
+ }
+ if (sbi->data_start_sector <
+ sbi->FAT1_start_sector + sbi->num_FAT_sectors * p_boot->num_fats) {
+ exfat_err(sb, "bogus data start sector");
+ return -EINVAL;
}
+ if (sbi->vol_flag & VOL_DIRTY)
+ exfat_warn(sb, "Volume was not properly unmounted. Some data may be corrupt. Please run fsck.");
+ if (sbi->vol_flag & ERR_MEDIUM)
+ exfat_warn(sb, "Medium has reported failures. Some data may be lost.");

/* exFAT file size is limited by a disk volume size */
sb->s_maxbytes = (u64)(sbi->num_clusters - EXFAT_RESERVED_CLUSTERS) <<
sbi->cluster_size_bits;

+ /* check logical sector size */
+ if (exfat_calibrate_blocksize(sb, 1 << p_boot->sect_size_bits))
+ return -EIO;
+
+ return 0;
+}
+
+/* mount the file system volume */
+static int __exfat_fill_super(struct super_block *sb)
+{
+ int ret;
+ struct exfat_sb_info *sbi = EXFAT_SB(sb);
+
+ ret = exfat_read_boot_sector(sb);
+ if (ret) {
+ exfat_err(sb, "failed to read boot sector");
+ goto free_bh;
+ }
+
ret = exfat_create_upcase_table(sb);
if (ret) {
exfat_err(sb, "failed to load upcase table");
--
2.25.1
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